1. Field of Application
The present invention is related to the building industry and deals particularly with an improved system for the enlargement of pre-existant buildings, in a gradual, simple and inexpensive way.
Such a system has been a long sought objective for low income families whose savings need be immediately used and maximized.
This system would prove to be not only desirable but necessary in countries with high demographic growth and a low income per capita.
Recently in Mexico and other contries the housing problem was worsened alarmingly due to such factors as population growth, lack of financial resources, scarce specialized labour and the rising cost of building materials.
In the case of Mexico, it is estimated that during the next ten years more than 8,000,000 low income families with hardly any access to credit will be in need of a dwelling. Therefore, the building of these dwellings will depend on the small amounts of capital saved by each family through a long period of time.
Thus, a great mass of effective demand will be characterized as an atomized demand. one which needs and can purchase small portions of a dwelling. To prove this point we only need to walk through any squatter settlement and see a multitude of construction signs pointing to the future development of the dwellings, specially obvious are: piles of building material, foundations without walls, walls without slabs, temporary constructions and the everpresent steelbars protruding from concrete elements.
In Mexico the public sector finances aproximatly 30% of the dwellings for low income families, while the informal or social sector is responsable for the other 70%.
The investment currently undergone by the public sector in projects concerning sites and services, progressive construction, and improved housing justifies the participation of large enterprises. Nevertheless, due to a lack of appreciation of the informal market and the traditional inertia in the building industry we find that products now on the marketplace do not address the problems and possibilities posed by the gradual growth of construction.
Likewise in the informal sector, the size and singularity of each atom of demand inhibits the intervention of specialists and the efficient solution of design and construction problems. In a similar way the owner generally depends on low qualified labour including his own, this results in a large waste of resources and poor quality construction.
2. Description of the Previous Technique
Recent studies in Mexico indicate that 80% of the dwellings built use one variation of the so called traditional system characterized by load bearing walls made with a variety of brick types, the walls are reinforced with horizontal and vertical elements of reinforced concrete, and floor slabs and roofing generally made of reinforced concrete.
Whatever applies for the traditional system is also valid for any future extension of the building. As a result the building of an extension usually follows the next sequence: first, foundations are built, then the brickwork conforming the walls is laid and the vertical concrete reinforcements poured, next the steel bars of the horizontal wall reinforcements are placed and the concrete slab is built. In some instances before the slab is built temporary roofing is installed which is substituted for the slab in a later stage. The same procedure will be followed for extensions in upper levels obviously skipping the foundations.
In this manner, with the traditional system the brickwork will remain unstable until the vertical reinforcements are poured, and the reinforcements can not be poured until all the concurrent walls are built. This implies that all foundations, brickwork and vertical wall reinforcements must be built in order to atain a load bearing and stable structure.
When building with the previous technique, qualified personnel are required to establish the right spatial references so that the construction fulfils a pre-established geometry. For this reason poorly qualified or unskilled labour like the owner himself must always work under the supervision of qualified personnel.
The building technique previously described presents a series of problems that are of the greatest importance when dealing with the gradual extension of a building, since it can not effectively use the small capital flows that feed the construction of the dwelling in a gradual way.
One of the main disadvantages of the extensions built with the previous technique comes from a large underemployed capacity, which is fully used years later when the building is finally completed.
Another disadvantage of the previous technique results from the order of execution, because the vertical wall reinforcements are poured after the brickwork is laid they can not be used to support the guiding string which allows for the correct placement of each brick, furthermore, the brickwork will remain unstable until the vertical reinforcements are poured.
Given the above, all the brickwork and the vertical reinforcements must be concluded in a relatively short period of time with the permanent presence of qualified workmen. Furthermore, due to the temporary instability of the brickwork there is a real danger to workmen and to personnel in the surrounding areas.
Although the improved system of progressive construction has been focusing specifically on the extension of dwellings it is obvious that this type of construction may be used for any other purpose.